Smooth Muscle Cells

Question 1

Characteristics of Smooth muscle cells

Answer 1

Spindle shaped, relatively small (about as long as a skeletal muscle is long)

Question 2

Actin/myosin ratio in smooth muscle cells

Answer 2

Greater in smooth (10:1) vs skeletal (2:1)

Question 3

What’s “missing” in smooth muscle cells?

Answer 3

Sarcomere, T-tubules, terminal cisternae, poorly developed SR. Lack hexagonal arrangement of actin/myosin

Question 4

SR in smooth muscle

Answer 4

Still a Ca++ source, needs extracellular Ca++ source for contraction

Question 5

Control of contraction in smooth muscle

Answer 5

Uses myosin-based control of contraction

Question 6

Actin binding proteins of smooth muscle

Answer 6

Caldesmon and Calponin. not primary control proteins in smooth muscle

Question 7

What is different about the troponin in smooth muscle?

Answer 7

No troponin -I to inhibit cross-bridge cycling

Question 8

Polarity of myosin in smooth muscle?

Answer 8

Side-polar striated

Question 9

Innervation of smooth muscle

Answer 9

Innervates by autonomic nervous system. No specialized nerve-muscle junction

Question 10

Single unit smooth muscle organs

Answer 10

Unitary/visceral smooth muscle. Many gap junctions between cells. Behaves in syncytial manner. Sparse innervation.

Question 11

Slow wave potentials

Answer 11

Spontaneous, graded oscillation in membrane potential that is rhythmical in nature, can lead to action potential

Question 12

Plasticity

Answer 12

Slow stretch of single unit organs leads to lengthier of smooth muscle. Aka stress relaxation

Question 13

Stretch induced contraction

Answer 13

Fast stretch cause depolarization and leads to contraction

Question 14

Multi unit smooth muscles

Answer 14

Each cell acts relatively independent of other smooth muscle cells in the organ. More in specialized muscles (eye, bronchial muscle, GI sphincters). Less gap junctions. Tend to have higher innervation ratios.

Question 15

High progesterone’ effect on smooth muscle

Answer 15

Reduces number of gap junctions in myometrial smooth muscle during pregnancy. Causes myometrium to behave more like non-innervated smooth muscle

Question 16

Rising estrogen levels at term of pregnancy

Answer 16

Causes smooth muscle hypertrophy. Increase in number of gap junctions. Myometrial performs more like single unit

Question 17

What complex triggers contraction in smooth muscle?

Answer 17

Ca-calmodulin complex

Question 18

High amounts of cAMP does what to smooth muscle?

Answer 18

Relaxes smooth muscle (inactivated MLCK)

Question 19

High Ca and MLCK

Answer 19

Causes contraction by increasing MLCK activity

Question 20

Tone definition

Answer 20

Constant and stable low level of contraction

Question 21

Latch state

Answer 21

Maintains tone without ATP expenditure.

Question 22

What is ATP required for in smooth muscle contraction?

Answer 22

Control (light chain phosphorylation ) and cross bridge cycling

Question 23

Smooth muscle Ca extrusion

Answer 23

3Na/Ca exchanger, SR Ca ATPase

Question 24

Phospholamban

Answer 24

Inhibits Ca ATPase

Question 25

What happens if PLB is inhibited?

Answer 25

Increase in contraction due to lack of inhibition

Question 26

L-type of Ca channel

Answer 26

Opens slowly, open at relatively positive membrane potential. Affected by Ca channel blockers

Question 27

T-type Ca channels

Answer 27

open and close quickly. Rapid influx from channels may be key to Ca-induced Ca release from the SR. Not blocked by usual Ca channel blockers

Question 28

Difference in electromechanical coupling between smooth and skeletal muscle

Answer 28

Smooth has both local-graded potentials and action potentials

Question 29

cAMP-dependant relaxation

Answer 29

β-adrenergic agonist, adenosine, PGI2. Can occur with or without Ca. PKA phosphorylates MLCK thus preventing Ca-calmodulin complex. cAMP can also decrease Ca in some cells

Question 30

cGMP-dependant relaxation

Answer 30

NO, ANP. cGMP decreases myosin light chain phosphorylation. changes to phosphatase (increased) and MLCK (decreased) are mediated by phosphorylation of cGMP dependent protein kinase

Question 31

Phospholipase-C dependent contraction

Answer 31

Angiotensin II, α₁-adrenergic agonist, endothelium. IP3 is formed/releases intracellular Ca. DAG is made/activates PKC. Can phosphorylate and number of proteins to cause contraction.

Question 32

ATP-sensitive K-channels

Answer 32

K channel that remains closed in the presence of normal intracellular ATP

Question 33

Ischemia's effect on intracellular processes

Answer 33

Decreases intracellular ATP, which opens the K-channels, and hyperpolarizes the membrane

Question 34

Hyperpolarization's effect on voltage gated L-type Ca channels

Answer 34

Closed the channels, reducing Ca influx, and relaxes smooth muscle

Question 35

G-protein-coupled K channel agonists

Answer 35

ACh on the m2 receptors and adenosine on A1 receptors. Interacts with a G-protein

Question 36

G-protein subunit's action on the K-channels

Answer 36

Bind directly to them and opens them. Cell is hyper polarized. L-type Ca channels are inactivated. Relaxation occurs